Separation fasteners which form part of a fastener system customarily utilize gas pressure as the power means for separation. The gas pressure is converted to a physical force that accomplishes the separation. There are two basic types of separation fasteners, classified by the mode in which the separation is attained. One is the tensile type, where an exerted force streches a portion of the fastener beyond its tensile capacity, and separation results. The other is the shear type, where a portion of the fastener is sheared from the remainder of the fastener. This invention relates to shear type separation fasteners.
It is a drawback of the known shear type fasteners that the force which must be exerted must be at least equal to the shear strength of the fastener. Thus, if the fastener's ultimate strength is determined by its resistance to shear forces at some critical location, then with conventional fasteners a force at least that great must be applied to effect the separation. This applied force constitutes a sharp shock on surrounding equipment, which it is best to minimize. However, reducing the area to be sheared for this purpose also reduces the strength of the joint, so there is little improvement possible by this means.
This invention applies the separation force in such a way as to reduce the force which must be applied to a level below the shear strength of the fastener, so as to maintain the same retentive capacity to resist shear loads, but this enables a separation to be made with a lesser shock.